In optical networks applying wavelength division multiplexing (WDM), an optical transport network (OTN) has been standardized as a framework. In the OTN, a plurality of types of client signals may be accommodated, and large-volume transmission may be performed. Japanese Laid-open Patent Publication No. 2008-113394 discloses an optical transmission system in which client signals are transmitted while being accommodated or multiplexed in optical transfer unit (OTU) frames in the OTN.
A difference in bit rate between an accommodated signal and a frame signal that accommodates the signal is compensated by asynchronously mapping the accommodated signal to the frame signal (asynchronous mapping procedure (AMP)). However, with an increase in bit rate and diversification of accommodated signals, generic mapping procedure (GMP) is being adopted. In the GMP, the number of pieces of data and the number of pieces of stuff to be accommodated in a frame accommodating portion are determined based on a difference in bit rate between an accommodated signal and a frame signal that accommodates the signal. The GMP is disclosed in U.S. Pat. No. 7,020,094.
For adopting the GMP and accommodating a frame signal that accommodates a signal in a frame signal having a bit rate higher than that of the frame signal, generation of optical data transfer unit (ODTU) frames is required.